View Full Version : Drive Ratios

11-12-2006, 04:11 PM
Hopefully someone here can enlighten me on drive ratios and gearing ratios. I have some stupid questions regarding them.

From my understanding, S/P*2.25=FDR (Spur/Pinion*2.25=Final Ratio).

So if I have a 75 spur paired with a 12 pinion, my radio would be a 14.06:1

I know there's ratios for different race types (on-road, off-road, dirt, so on and so forth).

My main questions are:

1. Does changing the final ratios make a difference in speeds?
2. Which type is best for the different racing types? (will a 6.98 be best for on road or would a 5.63?)

I know this prolly should go in the racing sections, but it's not related to my car at all :) Just a minor hobby I've rediscovered.

11-13-2006, 02:05 AM
I've never seen that formula. :shrug:

What I know is you divide the number of teeth on the driven gear by the number of teeth on the drive gear.
This gives you the gear ratio for that particular set.

For instance, if the drive gear has 10 teeth, and the driven gear has 20, you have a 2:1 drive ratio.

Changing the ratio will DEFINITLY change the speed of your car in that gear.
The numerically higher the number, the lower the top speed will be in that gear, but the faster your car will accelerate, assuming you have traction.

Same goes for final drive.

Example would be the RC vs regular ST185 trans.
The regular final drive ratio is 4.29:1
The RC is 3.93:1.

So the RC trans in the same car [the RC makes more power, making up for the different ratio] would have a slower acceleration, but a higher top speed.

As for what is best for what, it depends on where you are racing.
For drag, obviously a higher ratio will get you going faster.
If you are doing Nascar type stuff, you would want a lower ratio for a higher top speed.

11-13-2006, 02:13 AM
Awesome :)

Thanks. Yeah I was trying to refamilerize myself with drive ratios cuz of this here:

I have a full toolbox of drive and pinion gears (like 2 dozen of each), 4 different motors, and 6 sets of tires (1 asphalt racing, 2 asphalt driving, 3 offroad) The guy I got it from placed in 2nd place multiple times in on road races (have the placques too :)).